The present invention relates to polymeric hydrocarbon compounds having reactive borane groups at chain ends, or within the polymer chain, and methods of preparation thereof.
By way of background, telechelic polymers (i.e., polymers with functional groups at both chain ends) have proven to be a very interesting class of materials. They represent several potential uses, such as liquid rubber [Milkovich, R., et al., U.S. Pat. No. 3,786,116 (1974)]. In the past, these types of polymers were mostly prepared by terminating living polymers with suitable reagents in conjunction with the use of difunctional initiators [Tung, L. H., et al., U.S. Pat. No. 4,172,100 (1979)] [Kennedy, J. P., et al., U.S. Pat. No. 4,276,394 (1981] or functionally substituted initiators [Schulz, D. N., et al., J. Polym. Sci., Part A1, 12:153 (1984)]. The anionic, cationic and recently metathesis [Risse, W., et al., Macromolecules 22:1558 (1989)] [Crowe, W. E., et al., Macromolecules 23:3536 (1990)] living polymerizations are particularly preferred because these routes provide well-defined polymers with high degree of functional groups at both ends of the polymer chain. However, this process is very limited because only few monomers undergo living propagation.
It is known that olefins are interconvertible to other olefins in the metathesis reaction [Ivin, K. J., Olefin Metathesis, Academic Press, New York (1983)]. Usually, this exchange reaction is fast and reversible. In the case of polymer, with unsaturation in the polymer backbone, the metathesis reaction taking place in the backbone corresponds to a polymer chain breaking and reforming reversible processes. In most cases, the equilibrium conditions can be achieved and the average molecular weight of polymers becomes constant [Schrock, R. R., et al., Macromolecules 20:1169 (1987)]. This dynamic equilibrium has been applied in the degradation of polymer chains by mixing an unsaturated polymer with a small olefin molecular in a metathesis exchange reaction. The resulting products are low molecular weight polymers with some cyclic compounds [Hummel, A., et al., U.S. Pat. No. 3,558,589]. Streck extended the chemistry further by incorporating tis metathesis exchange reaction into the metathesis ring opening polymerization. With the use of organic silicon containing olefins in a ring opening polymerization of a cyclic olefin, the polymer with terminal silicon groups was obtained [Streck, R., et al., U.S. Pat. No. 3,929,850 (1975)]. However, the yield was generally quite low and the product usually contains some insoluble gel due to the side reactions. Moreover, the silyl end group is not a desirable intermediate as it is difficult to convert the silyl polymer to other functional polymers by simple mild chemical reactions.
Borane compounds are valuable intermediates in organic synthesis [Brown, H. H., Organic Synthesis via Boranes," Wiley-Interscience (1975)]. However, borane functional polymers are rare. In the past few years, a new functionalization chemistry using the intermediacy of novel borane monomers and transition metal catalysts, including Ziegler-Natta [Chung, T. C., U.S. Pat. Nos. 4,734,472 and 4,741,276)] and metathesis catalysts [Ramakrishnan, S., et al., Macromolecules 22:3181 (1989)] [Ramakrishnan, S., et al., Macromolecules 23:4519 (1990)] has been investigated. The advantages of this chemistry are (a) the stability of borane moiety to transition metal catalyst, (b) the solubility of borane compounds in hydrocarbon solvent (hexane and toluene) used in transition metal polymerizations, and (c) the versatility of borane groups, which can be transformed to a remarkable variety of functionalities. Many new functionalized polyolefin homo- and co-polymers, with functional groups located at the side chains, have been obtained based on this chemistry.
Borane containing polymers, with the borane groups located in the polymer backbone or at the ends of polymer chains, are very rare. One report [Chujo, Y., et al., Macromolecules 24:345 (1991)] has shown the polyhydroboration of .alpha.,.omega.-dienes and monoalkylborane to relatively low molecular weight polymer with borane groups located in the polymer chain. The compositions of the products are limited by the availability of .alpha.,.omega.-dienes. The spacer between two borons in polymer chain usually is quite small, less than 10 methylene units. On the other hand, the preparation of borane terminated polymer is very difficult. Only one example related to telechelic polyisobutylene [Kennedy, J. P., U.S. Pat. Nos. 4,316,973 and 4,342,849] has been shown. In this case, the process was very complicated, involving low temperature living polymerization of isobutylene with difunctional initiator and subsequent multiple step polymer modification.
The present invention overcomes the above-described disadvantages and limitations inherent with various borane-containing polymers and their methods of preparation. The invention presents new polymers having borane groups at the ends of their polymer chains, or within the chains, and methods of synthesis thereof.
The present invention describes polymeric hydrocarbons having a reactive borane group at chain ends or in the polymer chain. In addition, the polymer composition can cover most known hydrocarbon backbones and the borane groups can be extended to the less expensive borane compounds, such as diborane. In turn, the borane polymers are easily converted to a variety of other functionalities, under mild reaction conditions. A wide range of telechelic polymers, with various polymer backbones, polymer molecular weight and functionalities, can be produced.
An object of this invention is to develop hydrocarbon polymers having a reactive borane group at chain ends or within the polymer chain.
It is also an object of the invention to develop convenient methods of preparation of polymeric hydrocarbons with reactive terminal borane groups. These and other objects and advantages of the invention will become readily apparent from the following description and are particularly delineated in the appended claims. Advantages of the present invention over the prior art and a better understanding of the invention and its use will become more apparent form the following disclosure wherein are set forth, by way of examples, certain embodiments of the invention.